An Argument For Low SBU

You have a lot of choice when it comes to air seeders. Not only are there a variety of manufacturers offering unique designs, but you can also select row spacings — typically ranging from eight to 14 inches. That particular choice may be the most important one of all.

Selecting a wider row-spacing option means a lot of the seedbed is not being utilized, and that brings up this question: Will that affect yield? Can better results be achieved through keeping seed rows close together?

Guy Lafond, a research scientist with Agriculture and Agri-Food Canada at Indian Head, Sask., says row spacing should be of primary interest to no-till producers. Things may be different for those using conventional tillage, however. Lafond’s research with conventional tillage practices didn’t find any significant difference in yield when various row widths were compared in winter wheat, durum, barley and flax. “There was no advantage in tillage operations between four-, eight-and 12-inch spacing,” he says.

But Lafond points to one possible disadvantage of low seedbed utilization with conventional tillage practices. In a conventionally tilled field, the soil between seed rows has been disturbed. Leaving wider areas of disturbed soil unseeded may promote more weed growth, because wider spacing would reduce competition from the seeded crop over a significant percentage of the field. (Kevin Elmy makes this point in his argument for high SBU.) However, no specific studies have yet been done to confirm that, Lafond points out.


Under no-till conditions, Lafond found that wider row spacing can positively influence yield — simply because it offers growers the ability to direct seed through heavy crop residues and get good seed placement.

But to get the greatest advantage from wide row spacing, you need to start with stubble height. To make the best use of wider spacing, Lafond says growers should seed into standing stubble that is 12 to 14 inches tall and aim the seed row in between existing stubble rows. The tall stubble provides a beneficial microclimate for the young plants, and that gives them a real boost. “The microclimate benefits have been well demonstrated at the Swift Current Research Centre in cereals, pulse and oilseed crops,” says Lafond. “The yield advantages gained were astounding.”

Getting crop seeded into tall stubble is easier with 12-inch row spaces. Using precision GPS or the stubble-detector systems that some manufacturers offer, shanks can be kept between the previous season’s rows without the potential problem of plugging up from higher trash levels. With narrower row spacing, inter-row seeding is more difficult.

And taller, standing stubble tends to trap more snow over the winter, which means higher soil moisture levels for the following crop year. But if 12 inches are good, is even wider better?

“Our data shows you can go to 12 inches without any reduction in yield,” says Lafond. “There is very little (research) work on row spacing wider than 12 inches.”

A new study set to begin this spring at the research facility at Indian Head will be looking to change that. “We’re going to look at 10, 12, 14 and 16-inch spacing in oats. Hopefully we’ll add other crops in the following year,” he adds.

That research is timely as manufacturers are seeing a demand from customers for the wide opener spacing options they offer on new machines. Cory Beaujot of Seedmaster manufacturing at Regina, Sask., says roughly 80 per cent of the air seeders leaving their plant have 12-inch row spacing.

But according to Lafond, producers shouldn’t look at wider row spacing as a way to save on inputs. “In terms of seed, we find there is no savings that way. You still want to attain a desired plant population,” he says. And that can only be done by maintaining a consistent seed count per square metre of crop area, regardless of row spacing.

And Lafond says that carries over into fertilizer rates as well. “If you’re supporting the same yield, then the (fertilizer) requirements are the same,” he says.


A typical one-pass seeding and fertilizing operation through a no-till field causes more soil disturbance than in a field under conventional tillage, where conventional seeding equipment is used. That is because a seed opener passes more easily through the tilled soil and, therefore, causes less disturbance. In a no-till field, the soil is firmer. That means you get more soil movement behind the opener. In narrow row spacing, some of the disturbed soil from one row may cover a neighbouring seed row, which results in deeper seed placement than intended. Spacing openers farther apart eliminates that problem.

And just how much soil disturbance occurs depends to a large extent on what seed opener is used. Wider openers, of course, disturb more soil — and machines fitted with them require more horsepower to pull. But no matter what opener style is used, air seeders with wider row spacing generally have lower draft requirements, which means the same tractor can pull a wider seeder, which improves efficiency and reduces per-acre costs.

Lafond also points to one other factor in determining draft requirements, and that is the overall weight of seeders. Models with a heavier weight per foot of width will take a little more muscle to move across a field. That would be an even more significant consideration in rolling countryside.

Scott Garvey specializes in writing about tractors and farm machinery technology for publications in Canada and Great Britain. He’s also a former affiliate member of the Society of Automotive Engineers (SAE). He farms near Moosomin, Sask.

About the author


Scott Garvey

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.



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